04_Implementing Business Logic

8/14/2019 04_Implementing Business Logic

1/18

4Copyright 2007, Oracle. All rights reserved.

Implementing Business Logic


2/18

4-2 Copyright 2007, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to dothe following: Decide when to use a Session Bean

Describe how a Session Bean works Discriminate between stateful and stateless beans Describe how the EntityManager manages Entities Create a Session Facade Bean and Interface


3/18


What Is a Session Bean?

A Session Bean is a type of Enterprise JavaBean (EJB)that: Implements a business process

Represents a client and server interaction Has a short lifespan Lives in memory rather than in persistent storage Is used to create a Session Facade


4/18


sr.srdemo.business

Session Beans and JPA Entities

sr.srdemo.persistence

Products.java

ServiceRequests.java

Users.java

EJB 3.0 Session Facade Bean JPA Entities

Expose

ServiceRequestFacadeBean.java


5/18


What Session Beans Do

EJB 3.0 Session Beans: Contain persistence methods Implement JPA queries

Encapsulate business logic Are invoked directly by the client Use data and resources on behalf of the client


6/18


Stateless and Stateful Session Beans

There are two types of Session Beans: Stateless Session Bean (SLSB) Short-lived like HTTP request Is contained in a single method call Does not maintain client state

Stateful Session Bean (SFSB) Long-lived like a login May invoke many methods Maintains state between different requests

EJB container

Client 1

Client 2

Pool of SLSBsEJB container

Client 1

Client 2

SFSBs


7/184-7 Copyright 2007, Oracle. All rights reserved.

Life Cycle of a Stateless Session Bean

Ready

CreationDoes not

existDestruction

Method



Life Cycle of a Stateful Session Bean

Ready

Creation

Passive

ActivationPassivation

Does notexist

Destruction

Ready (in TX)

Commit or rollback

TX Method

Method

TX method

Timeout



Stateless Session Bean: Facade

@Stateless(name=SRPublicFacade") public class SRPublicFacadeBean implements SRPublicFacade,

SRPublicFacadeLocal{

@PersistenceContext(unitName="EJB_Model")private EntityManager em;

public Object mergeEntity(Object entity){ return em.merge(entity); }

public Object persistEntity(Object entity) {em.persist(entity);return entity;

}



Implementing JPA Queries

public List queryProductFindAll()

{ returnem.createNamedQuery(Product.findAll")

.getResultList();}

public Product findProductById(Integer findProdId);{return

(Product)em .createNamedQuery(Product.findProductById")

.setParameter(findProdId", findProdId).getSingleResult();}

}



Session Bean: Interface

package sr.model;

import java.util.List;import javax.ejb.Remote;

@Local public interface SRPublicFacadeLocal {

Object mergeEntity(Object entity);Object persistEntity(Object entity);List queryProductFindAll();

Product findProductById(Integer, findProdId);

}



Stateful Session Bean: Example

// CartBean.java package cart.ejb

import javax.ejb.Stateful;@Stateful(name="Cart")

public class CartBean implements Cart {private ArrayList items;

@PostConstructpublic void initialize() { items = new ArrayList(); }public void addItem(String item) { items.add(item); }

public void removeItem(String item){ items.remove(item); }public Collection getItems() { return items; }@Removepublic void dumpCart() {System.out.println("BYE!");};

}

2

1

3

4



EJB Client

An EJB client is a stand-alone application, servlet,JSP, or another EJB that accesses the bean.It can be a:

Local client Resides within the same Java Virtual Machine(JVM) as the bean

Passes arguments by reference to the bean Interacts with the EJB through methods defined in

the local interface Remote client

Is location independent Passes arguments by value to the bean Interacts with the EJB through methods defined in

the remote interface



Interceptor Methods and Classes

EJB 3.0 introduces the ability to create custominterceptor methods and classes that are called beforeinvoking the methods they intercept. Interceptors:

Are available for only Session Beans (statelessand stateful) and message-driven beans Provide more granular control of a beans method

invocation flow Can be used to implement custom transaction or

security processes instead of having thoseservices provided by the EJB container

Are a new feature whose implementation detailsare not fully defined and are subject to change



Creating a Session Facade Beanin JDeveloper

Select EJB Session Bean in the New Gallery. Select the Session Type: Stateless or Stateful. Select the Transaction Type: Container or Bean.

Select Generate Session Facade Methods. Select the Entity implementation.



Adding Methods to the Bean

Select which methods you want to implement. JDeveloper proposes:

Transactional methods

Named queries Choose interfaces:

Local Remote



Summary

In this lesson, you should have learned how to: Describe what a Session Bean does Describe what a Session Bean contains

Differentiate between stateful and stateless beans Describe how the EntityManager manages Entities Create a Session Facade Bean and Interface


18/18

Practice Overview:Developing Session Facade Beans

This practice covers the following topics: Creating a session facade Displaying data using a Session Facade Bean

04_Implementing Business Logic

Documents

Transcript of 04_Implementing Business Logic